Dual-Loop and Parity-Time-Symmetric Optoelectronic Oscillator with Strong Sidemode Suppression

A dual-loop and parity-time (PT) symmetric optoelectronic oscillator (OEO) is proposed to generate microwave signal with high sidemode suppression ratio. The parity symmetry is implemented with two optical carriers of different optical power, which are used to realize two coupled resonators in the parameter space of optical wavelength. The dual-loop architecture is implemented by adopting optical fiber of different physical lengths. The joint mode-selection mechanism of the dual-loop configuration and the PT symmetry will result in a strong sidemode suppression ratio, as compare to that when a single technique is used. In the experiment, a microwave signal with a frequency of 10 GHz and a phase noise of -112.4 dBc/Hz at an offset frequency of 10 kHz is generated. A high sidemode suppression ratio of 60.71 dB is achieved.